Means of providing air purging in piston pump



E. L. s'HAw 2,847,942

MEANS OF PROVIDING AIR PURGING m PISTON PUMP Aug. 19, 1958 Filed April 21, 1953 ra wa FC .52; I

INVENTOR. 3 EDWIN L. SHAW United States PatentO "ice MEANS OF PROVIDING AIR PURGING IN PISTON PUMP Edwin L. Shaw, Columbus, Ohio, assignor, by mesne assignments, to American Brake Shoe Company, New York, N. Y., a corporation of Delaware Application April 21, 1953, Serial No. 350,200

8 Claims. (Cl. 103--162) This invention relates generally to hydraulics and is more particularly directed to fluid pressure energy translating devices known in the trade as pumps and motors.

An object of this invention is to provide a fluid pressure energy translating device with simple means for purging the piston chambers of air during the initiation of the operation of the device. In the operation of hydraulic fluid pressure translating devices particularly of those employed as pumps, it becomes necessary to prime the pump at the initiation of operation so that the pump will deliver liquid. When a hydraulic pump is started, particularly after having been at rest for an appreciable length of time, its piston cylinders and the suction line leading thereto may be full of air or have a combination of liquid and air therein and it presents a problem to expel this air because it is highly elastic.

Hollow pistons are employed in certain types of hydraulic translating devices and these pistons do not displace all of the liquid from thepiston chambers when the pistons are moved to their innermost positions in the piston chambers. When such translating device is a pump and it is connected in a hydraulic, system and air is present in its piston chambers and the pump is started, the air will be compressed in the piston chambers on the exhaust strokes of the pistons and, when the piston chambers are brought into communication with the inlet ports, this air will have expanded to a pressure equal to the pressure at the inlet ports and no fluid will flow therefrom into the piston chambers. It will be understood, of course, that when ,the pump is first started some air may be displaced from the pump and its suction line into the high pressure side of the system, but because the pump is not adapted to compress gases to a high pressure it can not purge itself completely of air by pumping all of it into the high pressure side of the hydraulic system and some air will remain in its piston chambers to cause the results above described. The main object of this invention is to provide a hydraulic fluid pressure energy translating device with means for assisting in the removal of this air.

Another object of the invention is to provide an air purging passage in the valving mechanism of the pump and locating the entrance to this passage in such a position that communication will be established between the piston chambers and an exhaust region of low pressure (preferably, but not necessarily, atmospheric pressure), which in this instance is the interior of the casing of the device, when the piston chambers or the valving ports therefor are moving from the outlet or pressure port to the inlet port.

A further object of this invention is to so locate the entrance to the air purging passage, mentioned in the preceding paragraph, that the valving ports of the piston chambers will be disposed out of registration with the outlet or high pressure port at the time they communicate with the entrance of the air purging passage so that fluid from the high pressure port will not be vented to the exhaust.

2,847,942 Patented Aug. 19, 1958 It is a further object of the invention to so locate the entrance to the air purging passage that the piston chambers will have passed the lower dead center position of the cam or other motion imparting means, that is, the position in which the pistons have been pushed into the piston chambers to the greatest extent, and have initiated their movement in an outward direction, the

disposition of the air purging passage being such that purging passage with a check valve to limit the flow of fluid through such passage to the direction from the piston chambers to the casing and prevent reverse flow therethrough; this check valve will permit the valving ports of the piston chambers to register simultaneously with the entrance to the air purging passage and the inlet port without drawing fluid or air back into the piston chambers from the interior of the casing.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of embodiment of the invention is clearly shown.

In the drawings:

Fig. l is a longitudinal sectional view taken through a portion of a fluid pressure energy translating device formed in accordance with the present invention;

Fig. 2 is a vertical transverse sectional view taken Fig. 5 is a similar view taken through a modified form of the invention.

The pump shown in the drawings is of the axial piston type. It should be understood at this time that this type of pump has been illustrated for convenience only and that the inventionis applicable to pumps of other types.

The pump 20 includes a casing having a body section 21, a head section 22 and a ring-like extension 23, the end of this extension being closed by cap 24. The head 22 is provided with bearing means 25 for the rotatable reception of a shaft 26 which, at its inner end, is suitably connected with a cylinder barrel 27 having a plurality of piston chambers 28 formed therein, these piston chambers being parallel with the axis of the shaft 26. One end 30 of the cylinder barrel is disposed in sliding engagement with a valve plate 31, this plate being arranged between the end 30 of the cylinder barrel and the inner surface of the head 22.

As shown in Fig. 2, valve plate 31 is provided with arcuate inlet and outlet ports 33 and 34 which register with suitable passages formed in the head 22, these passages providing for the flow of fluid to and from the ports 33 and 34. The end 30 of the cylinder barrel is provided with valving ports 35 which establish communication between the piston chambers 28 and the ports 33 and 34 as the cylinder barrel revolves in the casing. To facilitate the rotation of the cylinder barrel, roller 3 bearings 36 are disposed between the exterior of the cylinder barrel and the interior of the extension 23.

The chambers 28 have piston elements 37 disposed for reciprocation therein, these piston elements serving to draw fluid from the inlet port 33 into the piston chambers as the pistons are moved outwardly with respect to such chambers and expel this fluid through the outlet port 34 when the pistons are moved back into the piston chambers. This reciprocation of the pistons is accomplished through the engagement of bearing shoes 38 universally connected to the pistons as at 40 and held in sliding engagement with an inclined cam surface 41 by a springpressed retaining disk 42.

The construction of the pump or motor so far de scribed is substantially conventional and a further description of the pump is believed to be unnecessary, it being sufficient to state that, as the shaft 26 and cylinder barrel 27 are revolved in the casing, the pistons 37 will be reciprocated in the piston chambers to transfer fluid from the inlet port 33 to the outlet port 34, and that the cam surface 41 is so disposed that the dead center positions, that is, the positions at which the reciprocation of the pistons will be reversed will be on a line extending across the cam surface 41 and through the axis of rotation of the shaft. This line, indicated by the letters A-B, is shown in Fig. 2 of the drawings in a vertical position. The port plate 31 is fixed in the device by a pin 32 (Fig. l) in a position, as shown in Fig. 2, wherein its ports 33 and 34 are rotated slightly in the direction of rotation of the cylinder barrel (counter-clockwise as indicated by the arrow in Fig. 2) to place more of each of the areas of the cam surface 41 which lies between the ports 33 and 34 at one side of the line A--B. This position of the valve plate causes the pistons to move an initial extent into and out of the piston chambers before the valve ports of the piston chambers register with the outlet and inlet ports respectively. This movement of the pistons as the chambers aproach the outlet port will initially increase the pressure in the piston chambers to that of the outlet port and prevent shock and the generation of excessive noise when registration of the valving ports with the outlet port is established. After communication between the valving ports 35 and the outlet port 34 is interrupted, the initial movement of the piston in an outward direction as the chambers approach the inlet port will cause the decompression of the fluid in the piston chambers before the valving ports register with the inlet port 33. This decompression of the fluid will also eliminate shock and noise.

When air is contained within the piston chambers 28, r

the distance moved by the pistons as the valving ports 35 move from the outlet port 34 to the inlet port.33 will be insufiicient to permit the complete decompression of the air since this fluid is more highly compressible than .the liquid used in the pump.

As previously pointed out, it is the object of this invention to provide means for purging the piston cylinders of air contained therein. To accomplish this object, the port plate 31 has a passage 43 extending thereinto from its edge. This passage terminates in an entrance port 44 which is disposed in the sealing surface of the valve plate in the path of movement of the valving ports 35 as such ports move from the outlet port 34 to the inlet port 33. In the first form of the invention illustrated, passage 43, hereinafter designated as an air purging passage, is a plain passage of small size. It is a known fact that air will flow through small passages more readily than oil or other liquid. As shown in Fig. 2, the entrance port to the air purging passage is located in the space between the outlet port 34 and the inlet port 33. Fig. 2 has the outline of a valving port 35 imposed thereon io. dotted line to show that the port 44 is spaced a greater distance from the outlet port 34 than the length of the valving port 35. Such ports will, therefore, have moved out of registration with the port 34 before communicating with the port 44. The port 44 is located relatively close to the bottom dead center position of the cam indicated by the line AB in Fig. 2. Due to this location of the port 44, the valving ports 35 will communicate with the port 44 immediately after the cam 41 has initiated the outward movement of the pistons 37.

It will be obvious at this time that any air in the piston chambers will be under compression and, when communication is established between the piston chambers and the interior of the casing by the air purging passage it will flow to the interior of the pump casing. If the air is entrained in liquid, some of the liquid may be discharged also. This flow of the liquid will facilitate the removal or purging of the air. Through the removal of the air, more liquid will be drawn into the piston chambers upon the outward movement of the pistons and the priming of the pump will take place more rapidly.

Since port 44 is disposed in such a position that valving ports 35 may register with entrance 44 at the same time they register with the inlet port 33, it might be possible for air or liquid to be drawn into the piston chambers through the passage 43 if the pump casing contains air; the purpose of the passage 43 might be defeated in this manner. It is, therefore, proposed to place a check valve 45 in the air purging passage to prevent flow of fluid in a reverse direction through this passage. A simple form of check valve includes a seat 46 against which a ball 47 is yieldably held by a spring 48, this spring being retained by a threaded sleeve 50. In the event reduced pressures are generated in the piston chambers 28 while the valving ports 35 register with the port 44, check valve 45 will prevent the flow of air from the easing into the piston chambers. It is obvious that the air purging passage could be directly connected with exhaust if such connection were found desirable.

While the form of embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow:

I claim:

1. In a hydraulic fluid pressure energy translating device of the type having a casing and slidably engaged relatively movable elements, one of said elements providing pumping chambers with valving ports and the other providing spaced inlet and outlet ports alternately communicating with said pumping chamber valving ports upon relative movement of said elements; the combination of an air purging port and passage means in one of said elements establishing communication between each of said pumping chambers and the interior of said casing when the valving port thereof is moving between said outlet port and said inlet port.

2. In a hydraulic fluid pressure energy translating device of the type having a casing and slidably engaged relatively movable elements, one of said elements providing pumping chambers with valving ports and the other providing spaced inlet and outlet ports alternately communicating with said pumping chamber valving ports upon relative movement of said elements; the combination of an air purging port and passage means in the element providing the inlet and outlet ports, such port and passage means establishing limited communication between each pumping chamber and the interior of said casing while the valving port thereof is moving between said outlet port and said inlet port.

3. In a hydraulic fluid pressure energy translating de vice of the type having a casing and slidably engaged relatively movable elements, one of said elements providing pumping chambers with valving ports and the other providing spaced inlet and outlet ports alternately communicating with said pumping chamber valving ports upon relative movement of said elements; the combination of an air purging port and passage means in the element providing the inlet and outlet ports, said port and passage means establishing limited communication between each pumping chamber and the interior of said casing while the valving port thereof is moving between said outlet port and said inlet port; said port being located a greater distance from said outlet port than the length of the valving port of a pumping chamber to prevent the connection of the outlet port to the interior of said casing.

4. In a hydraulic fluid pressure energy translating device of the type having a casing and slidably engaged relatively movable elements, one of said elements providing pumping chambers with valving ports and the other providing spaced inlet and outlet ports alternately communicating with said pumping chamber valving ports upon relative movement of said elements; the combination of an air purging port and passage means in one of said elements establishing communication between each pumping chamber and the interior of said casing when the valving port of the respective pumping chamber is moving between the outlet port and the inlet port; and a check valve in said air purging passage means to prevent fluid flow from the interior of said casing through said passage.

5. -In a hydraulic fluid pressure energy translating device of the type having a casing and slidably engaged relatively movable elements, one of said elements providing pumping chambers with valving ports and the other providing spaced inlet and outlet ports alternately communicating with said pumping chamber valving ports upon relative movement of said elements; the combination of an air purging port and passage means in one of said elements establishing communication between each pumping chamber and the interior of said casing when the valving port thereof is moving between the outlet port and the inlet port; and a pring pressed valve member in said air purging passage means to prevent fluid flow therethrough from the interior of said casing.

6. In a hydraulic fluid pressure energy translating device of the type having a casing and slidably engaged relatively movable elements, one of said elements providing spaced inlet and outlet ports and the other providing pis ton chambers with valving ports alternately communicating with the inlet and outlet ports upon relative movement of said elements; the combination of an air purging port and passage means in the element providing the inlet and outlet ports, said port forming the entrance to said passage means and being disposed in the surface engaging the other element, said passage means opening to the interior of said casing and serving to establish communication between each of said valving ports and its respective chamber and the interior of said casing as each valving port moves between said outlet and said inlet port; piston elements disposed for reciprocation in said piston chambers; and cam means inclined in said casing to impart reciprocatory movement to said pistons, the points on said cam means at which the motion of said pistons is reversed being between said inlet and outlet ports} 7. In a hydraulic fluid pressure energy translating device of the type having a casing and slidably engaged relatively rotatable elements, one of said elements providing spaced inlet and outlet ports and the other providing piston chambers with valving ports alternately communicating with said inlet and outlet ports upon relative rotation of said elements; the combination of an air purging port and passage means in the element providing the inlet and outlet ports, said port forming the entrance to said passage means and being disposed in the surface engaging the other element, said passage means opening to the interior of said casing and serving to establish communication between each of said valving ports and its, respective chamber and the interior of said casing as each valving port moves between said outlet and said inlet port; piston elements disposed for reciprocation in said piston chambers; and a flat cam surface disposed in said casing in an inclined position with respect to the axis of relative rotary movement of said elements, the points of said cam surface at which the motion of said pistons is reversed being between said inlet and outlet ports, and said air purging port and passage means being positioned to connect with the valve port of each chamber after the piston therein has reached its terminal point of movement into the cylinder.

8. in a hydraulic fluid pressure energy translating device, means providing a casing with a valving surface having spaced inlet and outlet ports; means supported in said casing in relatively movable sliding engagement with said valving surface, said last-named means providing a plurality of piston chambers with ports in the surface engaging said valving surface and alternately communicating with said inlet and outlet ports upon relative movement of said means; piston means disposed for reciprocatory movement in said piston chambers; cam means inclined in said casing to cause said piston means to move outwardly in said piston chambers while the piston chamber ports communicate with the inlet port and inwardly in said piston chambers while such piston chamber ports communicate with said outlet port; and port and passage means for purging air from said piston chambers between the times of communication thereof with said outlet and inlet ports, said port and passage means being disposed and arranged to establish momentary communication between consecutive piston chambers and the interior of said casing as the valve ports of said chambers move between said inlet and outlet ports.

References Cited in the file of this patent v UNITED STATES PATENTS 2,465,954 Wright Mar. 29, 1949 2,553,655 Herman May 22, 1951 2,642,809 Born June 23, 1953 2,737,899 Bonnette et a1. Mar. 13, 1956 FOREIGN PATENTS 956,823 France Feb. 7, 1950 

